The present invention relates generally to substrate processing, and more particularly to an apparatus for storing and moving substrate cassettes.
Semiconductor devices are made on substrates, such as silicon wafers or glass plates, for use in computers, monitors, and the like. These devices are made by a sequence of fabrication steps, such as thin film deposition, oxidation or nitration, etching, polishing, and thermal and lithographic processing. Although multiple fabrication steps may be performed in a single processing station, substrates must be transported between different processing stations for at least some of the fabrication steps. In addition, random substrates in a particular batch may be tested using metrology devices which require additional stations. Substrates are stored in cassettes for transfer between processing stations, metrology stations and other locations. Although cassettes may be carried manually between processing stations, the transfer of cassettes is typically automated. For example, a cassette may be transported to a processing station in an automatic guided vehicle (AGV), and then loaded from the AGV onto a loading platform in the processing station by a robot. Another robot may extract a substrate from the cassette and transport it into a processing chamber at the processing station. When the fabrication steps are complete, the substrate is loaded back into the cassette. Once all of the substrates have been processed and returned to the cassette, the cassette is removed from the loading platform and transported to another location by the AGV.
In order to ensure that the processing equipment does not sit idle, a nearly continuous supply of unprocessed substrates should be available at the processing station. Unfortunately, many processing stations can hold only a single cassette at the loading platform. Therefore, once all of the substrates in the cassette have been processed, the cassette must be quickly replaced, either manually or by an AGV, with a new cassette containing unprocessed substrates. Running such a just-in-time cassette inventory system requires either significant operator oversight or a large number of AGVs, thereby increasing the costs of the fabrication facility.
Therefore, there is a need for a method and apparatus which continuously supplies substrate cassettes to a processing system so that system down time is reduced or eliminated.
The present invention provides a method and apparatus for storing multiple cassettes at a processing station, ensuring that a nearly continuous supply of unprocessed substrates is available for processing and that the processing equipment does not idle. Multiple cassettes can be stored at a processing station in a front end support frame and a cassette can be moved to one of a plurality of vertically disposed docking stations where substrates are extracted and transferred to the processing equipment. An automation system is mounted or otherwise disposed on the frame to transfer cassettes between docking stations or between processing stations. In another aspect of the invention, cassettes can be transported between different processing stations without the use of an AGV.
In one aspect of the invention, an apparatus is provided which includes a front end frame having a plurality of vertically disposed docking stations and multiple cassette storage stations. An automated transfer assembly is preferably disposed adjacent the docking stations and the storage stations to move cassettes between the storage stations and the docking stations. Additionally, an automated transfer assembly can be located between processing stations to transfer cassettes between processing stations without the need for manual or AGV assistance. In another aspect of the invention, a method is provided for delivering a continuous supply of cassettes to a processing system. The method preferably includes providing a plurality of vertically disposed docking stations and multiple storage stations and moving cassettes between the storage stations and the transfer stations to ensure that substrates are continually supplied to the processing system. Additionally, a method is provided for transferring cassettes between processing stations to continue the processing sequence without the need for manual or AGV assistance.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.